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Introduction: Sometimes the soil conditions are very poor even at greater depth and it is not practical to construct even deep foundation. In such cases various methods of soil stabilization and reinforcement technique is adopted. The objective is to improve the characteristics at site and make soil capable of carrying load and to increase the shear strength decrease the compressibility of the soil.

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In the investigation done by S A Naeini and S M Sadjadi,(2008) ,the waste polymer materials has been chosen as the reinforcement material and it was randomly included in to the clayey soils with different plasticity indexes at five different percentages of fiber content (0%, 1%,2%, 3%, 4%) by weight of raw soil. Moreover an environmental concern is also included by utilization of waste plastic materials and they can be made useful for improving the soil characteristics and to solve problems related to the disposal of waste plastic material. Contd….

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California Bearing Ratio (CBR) : CBR test results indicate that with a small increase in fiber content CBR values can be increased and thus improve the properties of soft clays. In order to examine the effect of cement admixtures and polypropylene fibers on the CBR values of peat soil, index properties tests on the peat soil have been conducted. The tests include: water content, liquid limit, plastic limit, organic content, specific gravity and fiber content.

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The CBR test has been carried out on the stabilized peat soil (mixture of peat cement and polypropylene fibers) to investigate the increase in strength of the samples. Contd…. Fig.1 polypropylene fibers, (Kalantari, 2009)

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Stabilized peat soil samples with cement and polypropylene fibers were placed in the CBR mold for air curing for 90 days. CBR tests were performed on samples under both, un-soaked and soaked conditions. Contd…. Fig.2 Increase in CBR values-Different cement and polypropylene fibers content

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In order to cure the stabilized peat soil samples with cement and polypropylene fibers, air curing technique has been used. In this technique, the stabilized peat soil samples for CBR tests were kept in normal room temperature of 30±2°C and relative humidity of 80±5% without any addition of water from outside. Cement dosages: Curing procedure: For CBR (un-soaked and soaked) tests, each sample consists of peat soil at its natural water content added with 15, 25, 30, 40 and 50% cement by weight of wet soil, with and without polypropylene fibers as an additive.

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Percentage of polypropylene fibers Peat soil samples at their natural water content were mixed with different percentages of cement and polypropylene fibers and were cured in air for a period of 90 days and then CBR test was performed on them. The samples examined for this purpose were prepared by adding 5, 15 and 25% cement and 0.1, 0.15, 0.2 and 0.5% polypropylene fibers. The sample which showed the maximum value of CBR after 90 days of curing was chosen as the optimum percentage of polypropylene fibers for further evaluation of strength of the stabilized peat soil.

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CBR soaking test Based on the results of this test, all stabilized peat soil samples were submerged in water for at least 6 days before performing the CBR tests under soaked condition. Fig.3 weight increase during soaking time Effect of stabilization on CBR value Fig.4 CBR (%) values of undisturbed peat and different percentage of OPC and polypropylene fibers for the stabilized peat soil cured for 90 days

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2. Shear Strength Test: Shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that a soil can sustain. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts. Due to interlocking, particulate material may expand or contract in volume as it is subject to shear strains.

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Three clayey soils with different plasticity indexes used in the present experimental testes were obtained from the three parts of Iran named as (soil A, soil B, soil C) They are defined as high plasticity soils (CH) according to the Unified Soil Classification System. This experimental work has been performed to investigate the influence of Plasticity Index and percentage of waste polymer materials on the shear strength of waste polymer materials on the shear strength of unsaturated clayey soils. Contd….

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Contd…. Fig.5 Waste plastic strips Fig.6 Waste Tyre Rubber Chips For this purpose, clayey soils with different plasticity Indexes were used and mixed with different percentage of waste materials to investigate the shear strength parameters of unreinforced and reinforced samples in terms of direct shear test.

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3. Consolidation Test: Consolidation is a process by which soils decrease in volume. In order to assess the effect of random fiber inclusion on consolidation settlement, swelling and hydraulic conductivity, oedometer tests were Conducted according to ASTM D2435-96. It occurs when stress is applied to a soil that causes the soil particles to pack together more tightly, therefore reducing its bulk volume. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil.

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4. Swelling Test: Swelling soils, also known as expansive soils, are ones that swell in volume when subjected to moisture. These swelling soils typically contain clay minerals that attract and absorb water. When water is introduced to expansive soils, the water molecules are pulled into gaps between the soil plates. Fig.7 Variations of swelling with fiber content and length .

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5. Shrinkage Limits : The shrinkage limit (SL) is the water content where further loss of moisture will not result in any more volume reduction. Increase in the shrinkage limits means that longer fibers having greater surface contacts with the soil have shown greater resistance to volume change on desiccation. It can be said that random fiber inclusion improved the soil tensile strength very effectively, thus resisting shrinkage on desiccation. Fig.8 Variations of shrinkage limit with Fiber content and length.

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6. Desiccation Cracks: It is a common knowledge that clay soils can crack during desiccation. Oedometer rings were used to investigate the effects of random fiber inclusion on desiccation cracking of the soil. After molding, confining rings containing the specimen were placed in open air in the laboratory at a temperature of about 30°C. Samples were regularly weighed and when no changes in three consecutive measurements were observed, they were considered completely dried.

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Then, samples were used for observational examination of the extent of cracking. Observational examination of samples after desiccation showed that by increasing the fiber contents and lengths, the extent and depth of cracks were significantly reduced. Contd…. (a) Unreinforced sample (b) Reinforced sample Fig.9 Desiccation cracking:

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7. Hydraulic Conductivity: The hydraulic conductivity of a soil is a measure of the soil's ability to transmit water when submitted to a hydraulic gradient. The hydraulic conductivity of the fibrous soil is dependent on the fiber content, generally increasing with fiber content increase. Fig.10 : Hydraulic conductivity for various fiber contents.

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Conclusion The following conclusions are drawn: The soil stabilization with waste fibers improves the strength behavior of unsaturated clayey soils and can potentially reduce ground improvement costs by adopting this method of stabilization. The addition of randomly distributed polypropylene fibers resulted in substantially reducing the consolidation settlement of the clay soil. Length of fibers had an insignificant effect on this soil characteristic, where as fiber contents proved more influential and effective.

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Contd…. Fiber reinforcement significantly reduced the extent and distribution of cracks due to desiccation as observed by the reduced number, depth and width of cracks. These results show that it can be used for covering waste material in containments and also can be used for canal slopes. The most important point is the environmental concern regarding the effects of waste plastic in soil and the problems and threats that is related with their excessive usage and disposal. This gives an effective solution to waste treatment with the advent of soil reinforcement.